This legislation was a flash point in the history of New Zealand’s international relations. It derailed New Zealand’s defence alliance with the USA and Australia known as Anzus.

The Anzus Treaty, which had come into force on 29 April 1952, drew the three parties together over shared defence interests. Under Article II in the Treaty, they had agreed that ‘separately and jointly by means of continuous and effective self-help and mutual aid’, they would ‘maintain and develop their individual capacity to resist and attack’.

Increasingly, nuclear weapons and nuclear-powered military apparatus became integral to defence. The 1980s saw a proliferation of nuclear weapon, especially in the arsenals of the two major Cold War super powers, the USA and the Soviet Union. With this, fears increased about the potential global fall-out of nuclear war.

Locally, there were also specific concerns about the impact of nuclear testing in the Pacific. Anti-nuclear sentiments gained popular and political support, and saw New Zealanders elect a Labour-led anti-nuclear government, under David Lange, in 1984.

In 1985, the government said no to an American request for a visit to the country by the guided missile destroyer USS Buchanan. The basis for the refusal was that the Buchanan could potentially be carrying nuclear weapons. The US government, which would not confirm or deny this, retaliated by severing military ties and downgrading diplomatic ones.

Visits by vessels carrying weapons, or those that were nuclear powered, were specifically banned by the 1987 Act. Under section 11, ‘entry into the internal waters of New Zealand by any ship whose propulsion is wholly or partly dependent on nuclear power’ was prohibited. The statute also vetoed the acquisition, storage and testing of nuclear explosive devices.

The legislation finally ruptured the Anzus Treaty. The US suspended military cooperation with New Zealand, and demoted New Zealand to the status of ‘friend’ rather than ‘ally’. But four years after this expulsion, more than half of the New Zealand population still believed this sacrifice was worth it.